The number one complaint filed with both state and federal environmental agencies against animal producers involves odors. What is true for animal producers in general is also true for poultry producers. Controlling odors associated with poultry manure is a continuing problem for poultry and egg producers. Aerosol ammonia is one of the primary causes of nuisance odors associated with confined animal feeding operations. Since aerosol ammonia comprises a large portion of the odor associated with poultry litter, measures to control odor at poultry operations should incorporate strategies to reduce ammonia volatilization. In addition to ammonia's role as a component in nuisance odors, high levels of gaseous ammonia adversely affects animal health and the safety of people working in these environments.
Aerosol ammonia levels in hen houses with shallow pits and monthly manure removal have been measured to be in the range of 46 parts per million (ppm). Similarly, the levels of aerosol ammonia in hen houses with deep pits (manure-drying pits where manure is removed annually) have been measured to be in the 46 ppm range. Gaseous ammonia levels are especially high in winter, when hen house ventilation is restricted to conserve heat. During cold weather, gaseous ammonia levels in hen houses often exceed the 46 ppm range.
Poultry, for example, chickens and turkeys, continuously exposed to 20 (ppm) ammonia vapors exhibit significant respiratory tract damage after only six weeks. Chicks exposed to 20 ppm ammonia for 72 hours are much more susceptible to Newcastle Disease than chicks reared in ammonia-free environments. A high level of ammonia in the environment of laying chicken hens is also known to reduce egg production. For a more thorough discussion of the effect of high levels of gaseous ammonia on animal health and production, the reader is directed to the following articles that are incorporated by reference herein in their entirety. See: Avian Dis. 8:369-379, 1964; Deaton et al. Poultry Sci., 63:384-385, 1984; McQuitty et al. Canadian Agricultural Engineering 27:13-19; Strombaugh et al. J. Anim. Sci. 28:844, 1969. Similarly, high ammonia levels correlate with a reduction in the amount of animal feed converted to animal body mass and reduced weight gain in hogs.
In addition to ammonia's adverse effects on animal health, exposure to high levels of aerosol ammonia also adversely impacts human health. For example, exposure to aerosol ammonia concentrations in the range of 25 parts per million (ppm) produces discomfort in workers, and even brief exposures (<5 minutes) to ammonia can cause nasal irritation and dryness. In recognition of the ill effects of aerosol ammonia on human health, both the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) identify ammonia as a health hazard. Currently NIOSH rules set the permissible exposure level (PEL) for ammonia over an 8-hour period at 25 ppm. OSHA rules set a PEL, over an 8-hour period, at 50 ppm. OSHA also recognizes that an aerosol ammonia concentration of 300 ppm ammonia is immediately dangerous to life or health (IDLH). 29 C.F.R. 1910.120 (2003) defines IDLH as “[a]n atmospheric concentration of any toxic, corrosive or asphyxiant substance that poses an immediate threat to life or would cause irreversible or delayed adverse health effects or would interfere with an individual's ability to escape from a dangerous atmosphere.”
In addition to the problems associated with aerosol ammonia in animal manure, manure often times comprises high concentrations of water-soluble forms of phosphorus. High concentrations of phosphorus can cause environmental problems, especially if the phosphorus finds its way into surface water sources or shallow aquifers. Manures from monogastric animals such as hogs and poultry are especially high in phosphorus due to the inability of monogastric animals to digest phytic acid, a phosphorus-rich compound commonly found in animal feeds. The presence of high levels of soluble phosphates in manure is especially problematic when manure is disposed of by spreading it over fields or when feedlots are located near watersheds or above shallow aquifers. Examples of environmental damage caused by manures high in soluble phosphates include fish kills and bacterial or algal blooms exacerbated by the introduction of phosphates from manure into surface waters.
While plants require phosphorus in order to grow, excess levels of phosphorus can stunt plant growth and in some cases cause plant death. This is especially problematic, as one common means of disposing of manure is to use it to fertilize plants. Accordingly, phosphorus must be provided to plants in amounts conducive to and not detrimental to plant growth and development. When phosphates are provided to plants in amounts that exceed the plants' ability to absorb these compounds, excess phosphates accumulate in the soil or find their way into the watershed.
One widely used measure of fertilizer efficacy is the fertilizer's Nitrogen to Phosphate ratio (N:P ratio). For most plants, a N:P ratio in the 5.8:1 range is acceptable. When the N:P ratio is substantially lower than 5.8:1, a compound may provide more phosphate than plants can readily absorb while providing less nitrogen than the plants require for optimal growth. Off-gassing of ammonia lowers the nitrogen content in manure, thereby decreasing the nitrogen/phosphorus ratio in the manure. Especially if manure is already high in phosphorus, as ammonia is off-gassed the N:P ratio may become so low that the manure must undergo costly processing before it can be used as a fertilizer.
Clearly then, there is a need for methods to produce a manure that exhibits low levels of gaseous ammonia and has a N:P ratio in a range suitable for its ready use as a fertilizer.